Some teenagers do not like math or science simply for the same reason that some people don’t like peas and carrots. I suspect, however, that there are facets of the issue which are more complicated.
People in general and teenagers in particular need to be accepted by their peers. That being said, there is considerable pressure from other teenagers not to be interested in academia, e.g. math and science. To be sure, not a few number of adolescents consider trigonometry and organic chemistry the official currencies of “Nerdsville”. A significant amount of young people appear to be more interested in sports, socialization and extra-curricular activities which tend to draw their focus away from higher level mathematics and the sciences.
In looking at other causes, parental influences can not be ignored. Parents that are interested in math and science often raise their children to be. As the old saying goes, “the apple doesn’t fall far from the tree”.
Math and science are not subjects that the average person will grasp on his or her first attempt. There is a lot of visualization and abstract thinking that needs to occur before most people “get it”. This comes only through practice. Too many young people don’t apply themselves, give up too easily, don’t show the intestinal fortitude etc, and fail math and science as a result. This repeated failure only leads to frustration and ultimately a general disdain.